Steam trap valve assemblies of various types are known for use in steam piping assemblies in order to automatically drain water condensates, air and other gasses from the system without permitting the escape of steam. Water condensates form in steam piping systems as the natural result of the cooling of the steam as the letter gives up its heat in the performance of its function, i.e., heat transfer to a radiator, mold, etc. Such condensates, unless removed from the steam conduit, can build up in various areas of the conduit, such as at bends, fittings, low spots, etc., and can block the flow of the steam to produce shock waves or "water hammer" forces which can damage the conduit.
Also, air and other noncondensable gasses, such as carbon monoxide and dioxide, can build up in the steam conduit, reducing the steam temperature, insulating the heat-transfer system and/or producing corrosive acidic condensates.
Conventional steam trap valve assemblies are known for the automatic purging of steam piping systems of undesirable condensates and gasses while preventing the escape of steam. Reference is made to my U.S. Pat. No. 2,914,251 which relates to such a steam trap valve assembly containing a heat-sensitive bellows means which not only opens the outlet to drain condensate and dissolved gasses but also closes the inlet to prevent the further entry of steam to the steam trap when the bellows means becomes overheated, thereby preventing damage to the bellows.
Such known steam trap valve assemblies are dependent on the cooling and contraction of the bellows in order to cause opening of the outlet and release of the condensate and dissolved gasses. Repeated operation of the bellows results in wear, particularly in cases where the expanded bellows directly exerts the pressure which forces the valve closure member against the outlet port to close the outlet. Also, in such cases failure of the bellows can leave the system open to the escape of steam.
Some such assemblies are designed to fail to closed position for safety purposes. However, the closure of the valve causes water to accumulate in the valve and in the conduit, which water can eventually freeze and burst the valve assembly and/or the conduit.
While the safety function performed by a steam trap valve assembly is essential, it is desirable to provide a steam trap assembly in which the compressive forces exerted against the bellows in expanded position are reduced or removed. It is also desirable to provide a steam trap valve assembly which has a high water discharge capacity under normal operating conditions and which will remain open to the discharge of accumulated amounts of condensate and closed to the flow of steam without causing the bellows to contract to open the outlet. It is also desirable to provide a steam trap valve assembly which will continue to permit the discharge of condensate so as to prevent the accumulation of a sufficient volume of water in the valve assembly to cause any harm if it does freeze.
It is also desirable to provide a steam trap valve assembly which will balance the pressures within the housing and within the bellows compartment so as to prevent damage to the bellows caused by the pressure within the bellows compartment becoming substantially higher than the pressure within the steam trap housing.